US Preliminary Extended Weather thru Jan 12

Multi-Day Means Still Indicate A Transition Toward An Amplified Pattern Consisting Of An Ern Pac Ridge... Wrn-Cntrl Noam Trof...And Wrn Atlc Ridge By Late Next Week Into The Weekend. Assoc HgtAnomaly Centers By The D+8 Time Frame Have Been Fairly Consistent And Agreeable Over The Past Day Of Runs.

Teleconnections Relative To These Centers Continue To Indicate A Resulting Trend Toward Relatively Dry Conds With Below Normal Temps Over Most Of The West And Into The Plains Versus Wetter And Unseasonably Warm Weather Along/E Of The Ms River.

As This Pattern Develops Individual Models/Ensembles Differ In The Details But On Average Show Decent Agreement For A Days 6-7 Fcst. Ahead Of This Evolution There Is Still Significant Uncertainty With Energy Reaching The West In The Short Range Time Frame. However Enough Trending Has Occurred In Some Guidance To Yield Modestly Higher Confidence For Its Fcst Over The Ern 2/3 Of The Conus Versus 12-24 Hrs Ago.

Regarding This Leading System... The Past Couple Ukmet Runs And18z Gfs/Gefs Mean Show A Trend Toward Ecmwf Runs That Have Been Consistent In Bringing A Closed Low Aloft Newd Out Of Nrn Mexico Toward The Nern Quadrant Of The Conus.

The 18z Gfs And The New 00z Run Are Still Somewhat Faster Than The Ecmwf/Ukmet Though...And May Track The Feature Too Far Swd Over The Ern States In Light Of The Mean Ridge Fcst To Build Over The Wrn Atlc.

Interestingly The 18z Gefs Mean Has Adjusted Much Closer To The Ecmwf And Ecmwf Mean. The 12z Canadian And A Number Of Its Ensembles Are Still Quite Progressive But This Idea Is Now In The Minority. The 12z Ukmet May Eventually Become Somewhat Slow As It Shows More Wwd Elongation Of Upstream Pac Energy Than Seen In Most Other Guidance. In Light Of Increased Support For Some Variation Of An Ecmwf-Type Soln In Latest Guidance... Will Maintain Continuity With Previous Hpc Issuance That Emphasized Ecmwf/Ecmwf Mean Solns.

By Mid-Late Period An Average Of Model/Ensemble Guidance Captures The Most Agreeable Aspects Of The Trof Fcst To Amplify Into The West/Plains. Recent Gfs And Ecmwf Runs Appear To Display Similar Run To Run Variability In The Details. 12z Gfs/Ecmwf Runs Showed More Swwd Elongation Of The Trof Than Most Other Runs And Ensemble Means Though Not To The Point Of Being Outliers Relative To The Spread Of Individual Ensemble Members. Lagged Avg Fcsts From The Gfs/Ecmwf Point Toward A Mean Of Model/Ensemble Mean Fcsts. The Preferred Approach Yields A Good Compromise For Positioning The Wavy Sfc Front Fcst To Extend From The Grtlks Swwd Into The Plains By Days 6-7 Fri-Sat.

The Days 3-7 Fcst For Tue-Sat Is Based On A Blend Of 12z/4 AndPrevious 00z/4 Ecmwf Runs Plus 12z Ecmwf Ensemble Mean... Weighted Slightly More To The Operational Runs Thru Day 5 And A Little More To The Ecmwf Mean Thereafter.

This Blend Provides Some Account For Detail Diffs Within The Overall Ecmwf/Ecmwf Mean Scenario With The System Ejecting From Nrn Mexico And Offers The Desired Intermediate Soln Between The Two Most Recent Ecmwf Runs For The Amplifying Pattern Late In The Period.

Some Aspects Of The 18z Gefs Mean Are Also Reasonable But It Is Weaker Than Desired With Its Nrn Mexico/Srn Plains System Around Wed-Thu And With Grtlks Low Pressure By Sat.

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